Level of detail in System Requirements

Question

I've read in multiple places that the requirements must not be influenced by solution and must not contain solution. So in the below example , please can you help in letting me which is correct -

Application A is interacting with Application B to install a new service / change the service type and disconnect a service. There 3 different service types 1,2 and 3. Application B does not support changing service from 1 to 2 or 1 to 3. Hence 1 must be disconnected and then 2 and 3 must be added. However service can be changed from 2 to 3 or 3 to 2 directly.

In the above case , changing the service from 1 to 2 or 1 to 3 is a system level contraint. However from an end user's perspective this is a service change.

In the above case , should I have a single system requirement stating system shall allow service to be changed for all the service types supported or should I have 2 different system requirement - 1 stating which all services can be upgraded directly and the 2nd stating in which cases service needs to be disconnected and installed?

Answer 1

Requirements are that and only that: what is the required outcome for the system in question?

In this case, the System Requirements appears to be:

Application A must be able to:

• install a new service of type 1, 2, or 3
• change the service type of an existing service of type 1, 2, or 3
• disconnect a service of type 1, 2, or 3

in Application B

Requirements should be stated positively whenever possible, and phrased so as to be testable.

The specific implementation problems described are not part of the requirements. They are part of the design constraints.